The present invention relates to a decompression device for a hand starting four-cycle engine, and more particularly to the decompression device for a small utility engine used for a hand sprayer and a brush cutter.
Heretofore, the two-cycle engine is employed for the portable machine such as the hand sprayer, the brush cutter, and the like. However, the two-cycle engine has defects that exhaust noise is large, and the quantity of hydrocarbon in exhaust gases is large.
Therefore, the employing of the four-cycle engine is considered. The four-cycle engine has been improved in miniaturization and weight reduction. Such a small four-cycle engine is manually started with a recoil starter in general. Namely, the crankshaft of the engine is rotated by pulling a wire of the recoil starter.
The decompression device is provided in the small hand starting four-cycle engine so as to open slightly the exhaust valve in the compression stroke for decreasing the compression pressure in order to reduce the manual force at the cranking operation.
In order to temporarily open the exhaust valve, the decompression device has a complicated mechanism for temporarily operating the cam mechanism for operating the intake and exhaust valves. Therefore, the decompression device hinders miniaturizing the four-cycle engine.
On the other hand, cams for operating the valves are separately provided for the intake valve and the exhaust valve in order to exactly control the opening operation of the valves. There is a problem of how to mount the decompression device on the engine.